It has been reported previously that there exists a correlation between the metastasis of human melanoma cells and the amount of ICAM-1 (intercellular adhesion molecule-1) these cells express on their surface. Several investigators have suggested that this adhesion molecule may play a role in the migration of these cells. We have observed that the expression of ICAM-1 on several melanoma cell lines can be enhanced by simply growing more cells per area. Preliminary experiments, using the human melanoma cell line, A375, revealed that these cells constitutively produce a factor which is able to augment ICAM-1 expression. In addition, numerous experiments have shown that this activity is not due to many of the factors which are reportedly produced by human tumor cells such as PDGF, bFGF, TGF-alpha or TGF-beta. Work aimed at isolating and identifying this factor is currently in progress.